A few days ago, I had my macbook pro freeze completely. Upon restart, I was greeted with a probationary sign (circle with slash). A few looks online and it became clear that it was an issue with my recent upgrade to Mountain Lion. I was told to repair and verify all disks through my snow leopard disc. Everything appeared to be ok. I restarted my computer and went to erase the hard drive to find that disk utility said I had no hard drive. The only thing that showed up was my DVD drive and the disc inside my DVD drive. After 12-13 hours of trouble shooting, my mac randomly loaded up my desktop (which is proof that I actually do have a hard drive). It froze constantly, so I decided to restart and insert my OSX disc. My hard drive appeared this time and I got to erasing it. I was planning on doing a clean install this time. Halfway through my snow leopard installation process, the installation stopped and it told me to restart my mac. Upon restarting, I HAD NO HARD DRIVE. OSX asked me to pick a disk in which to install my OS on, and there is no disk to choose! So now, I've got a Macbook pro with absolutely no OS on it. It's unable to have an operating system installed on it due to it not reading my hard drive correctly. All that shows up in disk utility is the DVD drive. I'm hesitant and saying it's a Hard Drive problem as my hard drive disappeared randomly and then reappeared, just to disappear again. I do know that my HD re appeared because I logged into the desktop of my macbook though. Urgent help would be much appreciated!